BOSTON -- On his free-agent visit to New England in the spring of 2003, safety Rodney Harrison sat in Bill Belichick's office and became an instant believer.

At 30, Harrison was coming off an injury-plagued season with the Chargers that had inspired a host of can-you-still-play questions from his previous free-agent suitors.

Belichick, however, had a statement instead of a question. He told Harrison that he knew he could still play. And the Patriots' head coach was basing some of his belief on a hit the two-time Pro Bowl safety made when the Patriots visited San Diego the previous season.

Here's what floored Harrison: The hit that Belichick was referencing came during pregame warm-ups.

"He said, 'Man, you came up and you hit this guy so hard and knocked his helmet off,' " Harrison said. "I said, 'Coach, you remember that? You saw that?' After that, I knew I was there. ... That type of attention to detail is Belichick. He remembers everything. I was warming up. I was warming up. OK? I mean, are you kidding? I was like, 'This is tremendous. Who does that? Who remembers that? Sign me up. I don't care what they pay me.' "

Nearly a decade later, Harrison, an NBC studio analyst who played six seasons for Belichick, is eager to see what defensive game plan his detail-obsessed ex-coach will unveil when the Patriots host the 49ers and their precious quarterback, Colin Kaepernick, on Sunday night.

It's a compelling story line - the wizard versus the wunderkind: a 60-year-old coach with three Super Bowl titles scheming against a 25-year-old hotshot making his fifth career start. Listen to the opinionated and passionate Harrison long enough and you'll become convinced Belichick already knows everything from Kaepernick's favorite spot in the pocket to his favorite spot for lunch.

Of course, Harrison isn't alone.

"Bill Belichick is one of the best defensive coaches in the history of football," NFL Network analyst Joe Theismann said. "So you have to assume that he's going to have something that Colin has never seen on film."

At this point, it probably should be noted that Belichick won't be making any tackles Sunday night. And he'll be entrusting a defense ranked 26th in yards allowed per game (376.3) and 29th in passing yards allowed (275.5) to execute his game plan.

The Patriots, however, have clearly benefited from a midseason secondary shakeup. On Nov. 1, they traded for Tampa Bay cornerback Aqib Talib, a move that allowed them to shift cornerback Devin McCourty to safety.

In the Patriots' first four games with Talib, quarterbacks have a 72.4 passer rating against them, with three touchdowns and five interceptions. In the season's first nine games, opposing signal-callers had a 97.3 rating with 19 touchdowns and 10 interceptions.

In Monday night's 42-14 win over Houston, the Texans, who entered averaging 29.3 points a game, had seven points in the first 57 minutes, and quarterback Matt Schaub had his third-lowest rating of the season (68.8).

"Early in the season, in terms of defensive game plans, they were struggling, and they would be very vanilla in their scheme," Harrison said. "They wouldn't show a lot of things, and Bill just wanted them to play simple coverages they couldn't blow.

"Now that defense is clicking. Now they're creating turnovers. Now he has more confidence in them, and now he's starting to dial up more blitzes and different looks. Now you see these guys playing with a little swagger and confidence. It's no longer a liability; it's a tough defense."

And that tough defense will face a migraine-inspiring assignment in Kaepernick, who can stretch defenses with his arm and scare them with his legs. Kaepernick is averaging 8.3 yards per pass, which would rank third in the NFL if he had the required number of attempts. He's also averaging 7.6 yards a rush and has ripped off a pair of 50-yarders the past two weeks, the longest in franchise history.

Perhaps most important, his decision-making has matched his dazzling physical skills: He has thrown one interception among 129 passes during his NFL baptism.

Harrison, who played with Jim Harbaugh from 1999 to 2000 with the Chargers, said his former teammate didn't do opposing defensive coordinators any favors by inserting Kaepernick over Alex Smith.

"When you have a guy that talented, why wouldn't you?" Harrison said. "You'd be an idiot not to play him. When I game-plan against Alex Smith, 'OK, let's stop Frank Gore. OK, maybe there's such-and-such in the slot. Maybe we'll double-team (Randy) Moss when he comes in on 2nd-and-14 just in case there's a deep ball.' It's a simple game plan.

"But you have to game-plan against Kaepernick, plain and simple. You have to take him into consideration. Who's going to spy him? Where are we going to blitz him? Are we going to keep him in the pocket? He changes everything."

With that said, Harrison believes Belichick can befuddle the budding star.

Friday, Belichick, again demonstrated his attention to detail. While meeting with the New England media, he not only remembered an onside kick David Akers had against the Patriots, but he also recalled the precise year he kicked it (2007). And, in further discussing San Francisco's special teams, he highlighted deep-on-the-depth-chart names such as Tramaine Brock and Larry Grant.

If there is a yet-to-be-uncovered weakness in Kaepernick's game, Harrison says, his former coach will be the one to uncover it.

"He does not overlook anything," Harrison said. "He'd say, 'Hey, Rod, remember the first time we played Miami, you missed that sack.' I'm like, 'How do you remember that? You watch 10,000 plays a year and you remember me missing a sack?' I'm telling you, that's what makes him great."

49ers at Patriots

5:20 p.m., Channel: 11 Channel: 3 Channel: 8 (680, 107.7)

Spotlight on: CB Carlos Rogers. He was a Pro Bowl player last year, but, at 6 feet,192 pounds, Rogers' strength isn't covering quick and shifty wide receivers. This brings us to New England's Wes Welker, who specializes in slipperiness. Welker could make Rogers wish he were matched up in the slot against the Giants' Victor Cruz or Rams' Danny Amendola, who combined for 17 catches, 160 yards and a touchdown in two games against the 49ers this season. Welker, who has 95 catches for 1,116 yards, leads the NFL in receptions since 2007 with 649, 74 more than his closest pursuer. As they have done against Cruz, the 49ers could shade a safety over to Welker's side of the field to provide Rogers with assistance. Welker-sized practice-squad receiver Chad Hall played the scout-team role of New England's four-time Pro Bowl receiver during the week before he was released by the 49ers on Friday.

Injury notes: 49ers - WR Mario Manningham (shoulder) is doubtful, meaning first-round pick A.J. Jenkins will play in his second career game. Jenkins had eight offensive snaps last week and was not targeted with a pass. Patriots - All-Pro TE Rob Gronkowski is listed as questionable but reportedly will not play. Gronkowski broke a bone in his forearm Nov. 18.

The Big 3

-- Have you heard this game pits a really good offense against a really good defense? It's true. The Patriots have scored at least 30 points in 16 of their past 21 regular-season games. The 49ers haven't allowed 30 points in any of their past 31 regular-season games.

-- Michael Crabtree has been targeted 20 times over the past two weeks, 11 more than Colin Kaepernick's second-favorite target over that span (Randy Moss). There's a reason Kaepernick is feeding Crabtree: He has caught 16 of those 20 passes for 194 yards. Crabtree, who is on pace for 937 yards, is bidding to become the 49ers' first 1,000-yard wide receiver since Terrell Owens in 2003.

-- The Patriots have won 20 straight home games in December, a streak that dates to a 30-17 loss to the Jets on Dec. 22, 2002. San Francisco center Jonathan Goodwin was a rookie on that Jets team.